1. Field of the Invention
The present invention relates to a vehicle motion control method and vehicle motion control apparatus for controlling the steering of the vehicle or controlling the drive power of the vehicle based on a steering characteristic obtained according to the amount of a vehicle behavior which is generated around an axis in the vertical direction of the vehicle.
2. Description of the Related Art
According to a conventional technology for estimating the vehicle steering characteristic such as over-steer, under-steer and neutral-steer, for example, a front wheel slip angle βf and a rear wheel slip angle βr are estimated based on a vehicle velocity V, actual steering angle δ and the like using a two-wheel model as shown in FIG. 15 and then, the amount of vehicle behavior is estimated from a differential (βf−βr). According to another example of the conventional technology, the amount of the vehicle behavior is estimated from a differential between an object yaw rate computed using the same model and an actual yaw rate outputted from a yaw rate sensor (patent documents 1-3). These steering characteristics are used by a system which enhances the behavior stability of a vehicle by carrying out feed-back control based on the amount of the vehicle behavior.
[Prior Art]
    JP HEI5-294173 A(pp. 2-12, FIGS. 1-4) is incorporated herein by reference.    JP HEI7-25256 A (pp. 2-7, FIGS. 1-12) is incorporated herein by reference.    JP 2000-142362 A (pp. 2-6, FIGS. 1-3) is incorporated herein by reference.
According to the conventional technology for estimating the steering characteristic by using such a vehicle two-wheel model, the steering characteristic is estimated from a differential between an object vehicle yaw rate which is generated when a vehicle driver turns the steering wheel and an actual yaw rate which a sensor obtains by detection. As a result, the processing for determining the steering characteristic is executed with a delay. Thus, there is such a problem that this delay can become a technological obstacle to securing the behavior stability rapidly in a system which obtains the behavior stability of a vehicle based on the steering characteristic.
Further, because the processing for determining the steering characteristic is executed with a delay in the system for obtaining the vehicle behavior stability, there is a problem that a skilled vehicle driver who has acquired a high-level driving skill may be provided with steering feeling as if a counter steering action at the time of steering operation upon cornering is controlled with a delay. This is the same as when the steering characteristic is estimated by obtaining a differential (βf−βr) of the slip angles in the front and rear wheels.
On the other hand, in the system for enhancing the vehicle behavior stability by executing feedback control based on the steering characteristic and the amount of the vehicle behavior, the control for raising the responsiveness of the feedback control may intensify the over-steer. Therefore, there is another problem that securing of the vehicle behavior stability may be obstructed.